There are various types of prior proximity sensors employing ultrasonic, infrared ("IR"), or electrical measurement techniques. Ultrasonic and IR sensors make proximity measurements based on reflections of ultrasonic and IR radiation. Such sensors are, however, disadvantageous in some applications because of their relatively high cost and directionality.
Electrical sensors are of various types including inductive and capacitive proximity sensors, which make measurements based on sensing a frequency change, operating regime change, or absorbed current change of an oscillator having a feedback circuit that includes the sensor. However, such electrical sensors may have at least one of the following disadvantages:
They do not provide a direct analog measurement, such as a voltage or current level, at their outputs; PA1 they are highly susceptible to external electromagnetic fields; PA1 they have limited sensitivity, particularly to nonmetallic objects; PA1 they operate poorly in the vicinity of objects that have magnetic properties and/or are good electrical conductors; and PA1 they have poor high-frequency response that limits their ability to sense rapid movements and are, therefore, not useful in many biomedical, virtual reality, multimedia, and industrial applications.
What is needed, therefore, is a low-cost position and movement sensor capable of sensitively detecting metallic and nonmetallic objects and providing a direct output representing the movement, presence, or proximity of such objects.